Cross Contamination: the Risk and the Reality

It's been a decade since OSHA issued its Bloodborne Pathogens Standard (BPS) outlining procedures to protect employees from occupational exposure to bloodborne pathogens such as HIV and hepatitis B. In addition, the American Dental Association, Centers for Disease Control and National Association for Dental Laboratories have issued protocols for infection control procedures.

Despite these recommendations and the fact that it's best to eliminate cross contamination at the source—the dental office—labs report that although more clients have been disinfecting over the last several years, a large percentage still aren't disinfecting at all. Of those that are, the methods and materials used vary widely from practice to practice. "We still receive impressions wrapped in a brown paper towel with no bag, alginates that haven't been rinsed and impressions with dried blood or ones that are just sprayed with Lysol," says Scott Mappin, owner of Mappin Laboratories in Essex Junction, Vermont.

There are a number of reasons why more dentists aren't following disinfection procedures. For instance, improperly trained staff, concentration of energy and resources on operatory infection control procedures, concern about distortion and an "it's-the-laboratory's-responsibility" attitude. "There are still a lot of people out there who are looking the other way, both in labs and in dental offices. They have their heads in the sand and that's not a good place to be," says Charles Selser, president of 12-employee Selser Dental Laboratory, Terrytown, Louisiana.

True, there is little factual data—just plenty of industry folklore—on the risk cross contamination poses to the dental technician. However, health and safety experts say that it's precisely because the level of risk is unknown that you shouldn't take chances when handling potentially infectious materials.

Dr. Robert Runnells, former director of the University of Utah School of Medicine's dental infection control program, points out that it's difficult to prove cross contamination. "There have been a few controlled studies that show transmission of infectious organisms from the mouth but it's hard to prove that people were actually infected by transmission, especially because the incubation period for some diseases is so lengthy," he says. "However, there are cases of people being infected that have been traced back to the dentist. Anyone who ignores standard procedures is risking two things—potential infection and litigation." Runnells is also a retired author, consultant and lecturer on infection control.

Mary Borg, president of Safelink, a health and safety consulting company in Gainesville, Georgia, agrees. "Diseases are out there. One in 12 patients has some sort of infection, from the common cold to hepatitis," she says. "They can be a risk and employers must take precautions to protect themselves, their employees and patients."

High-risk areas

In the laboratory, there are three main areas of concern:

Impressions. Ideally, the dentist is sending impressions that are rinsed, blood- and saliva-free, properly disinfected, bagged and separated from the prescription. Since this isn't always the norm and because OSHA's Bloodborne Pathogens Standard mandates that laboratories disinfect all incoming cases, most lab owners accept non-disinfected cases and don't make discussing disinfection a priority with their clients.

However, you should draw the line at bloody impressions. "Blood has the highest concentration of contaminants compared to all other body fluids; saliva is farther down the scale," says Runnells. "Labs need to be much more careful when handling cases that have evidence of blood." In fact, some laboratory owners like James Thompson, Thompson Dental Laboratory, Wheaton, Illinois, simply refuse to accept bloody impressions. "If I received a bloody impression, I would definitely get on the phone with the doctor. It's totally unacceptable in today's world," says Thompson.

In addition, be careful when trimming back an impression. This is the most common place for a post-exposure incident, says Borg. If a technician cuts himself and there's blood on or in the impression, it could go directly into the blood stream.

Removable appliances—including denture repairs or relines, partial dentures or orthodontic appliances—present a risk of cross contamination since they have been in the patient's mouth and are made of acrylic that absorbs moisture. When the technician cuts or grinds away the layers, he can be exposed to bacteria. "Without a doubt, there's a high risk in a removable department or lab," says Selser. "If the pan or polishing materials are not properly cleaned and disinfected, you can cross contaminate Mrs. Jones' denture with Mr. Smiths'. Disinfection is critical."

Clinically poured models. If the dentist-client did not disinfect the impression first, he is potentially transferring infectious fluids to the model. Once the model is die trimmed in the lab, bacteria, virus or other organisms inside can become airborne.

Similar to visibly bloody impressions, it's critical to communicate with your dentist-clients if they are pouring up their own models. Find out if the impressions are being properly disinfected prior to pouring the model. You may want to consider providing him with your preferred disinfection method. Or, if he's pouring the models because he's using an alginate impression material, consider steering him to a new type of material so you can pour the models at the lab. That way, you'll be sure that disinfection is done properly.

For advice on disinfecting impressions, removable appliances and clinically poured models, see How to prevent cross contamination below.

Costs and benefits

Between solutions, protective equipment, training and labor, what does the average laboratory spend on disinfection? Safelink estimates that in its first year, a five-employee lab pays approximately $6 a case for infection control, including product costs, administrative costs, biohazard waste and labor. "When the laboratory determines its infection control costs, it has to incorporate them into its fees," says Borg.

The company—which consults with about 200 laboratories—is seeing more and more labs adding a line item for infection control to their invoices and standardizing procedures to help reduce processing time in the receiving area. One of Borg's laboratory customers provides his dentist-clients with case boxes and biohazard bags. "If a case comes into the lab without the provided packaging, he charges that client $1.50 for the extra time and labor it takes for the technician to process the case," says Borg.

Greg Thayer, owner of Thayer Dental Laboratory a 53-employee laboratory in Mechanicsburg, Pennsylvania, also estimates that his cost of infection control is between $5 and $6 to disinfect each case, including labor, materials and supplies. He factors the cost into the lab's overall fees.

Despite the costs, laboratories with top-notch disinfection procedures are marketing their services to dentist-clients and using them to enhance their professional images.

Your effort can be as simple as a letter, like the direct mail campaign Mappin used to inform his clients about the lab's new disinfection procedures. Other labs provide their dentists with infection control materials at no charge. Drake Precision Dental Lab, Charlotte, North Carolina supplies its dentist-clients with shipping boxes and sealable bags—with a separate pocket for the prescription—in which to place their impressions.

Selser Dental Laboratory markets its Aseptic Control Center—a separate area in the lab staffed only by three technicians specifically trained in ADA, CDC, OSHA infection control procedures. The 10-foot-long area consists of cabinets stocked with disinfection products and supplies, a sink, strainer pan and an area for waste disposal.

Thayer takes a similar approach by making it a point to take visiting dentists and surgeons through the lab's disinfection station. The lab also puts a "Germ Busters" logo on every case that goes back to the dental office. "It lets them know what you're providing to them is disinfected and serves as a reminder to the office to disinfect as well," says Thayer.

How to prevent cross contamination

Whether you're working with incoming impressions, removable appliances or clinically poured models, it's essential to practice the protocols to prevent cross contamination at all times in the laboratory. Here are some basic practices to adapt into your daily routine:

Disinfect surfaces. Any surface that comes into contact with potentially infectious materials must be cleaned and disinfected with an EPA-approved chemical agent or a hospital-grade surface disinfectant. Dr. Rella Christensen, PhD, director of Clinical Research Associates (CRA), Provo, Utah, recommends the following method: use a 4x4 cotton-filled gauze sponge soaked until dripping with disinfectant. Wipe the surface for two minutes. Take a second, clean gauze sponge soaked with disinfectant and scrub away any remaining debris. Wipe the surface with a clean paper towel.

Wash your hands frequently. "Hands are well documented as a major source of cross contamination—to other people and other objects," says Christensen. "Technicians should be washing their hands throughout the day with some type of good antimicrobial, not just soap." One option, says Christensen, is using a 4% chlorohexidine hand wash liquid for 15 to 30 seconds, rinsing thoroughly and drying with a single-use paper towel.

"Put a barrier between you and the bacteria," advises Les Hochhauser, director of product development for American Dental Supply, Easton, Pennsylvania who lectures on health and safety in the laboratory. Wear proper protective equipment like gloves, fluid-impervious robes, masks and eye shields when necessary.

Disinfection procedures

Evidence of blood. Ideally, cases with evidence of blood should be returned to the dentist-client. If you choose not to return the case, it's vital to know that a CRA study has found that more than half of the 10 active ingredients used in disinfectants don't work in the presence of blood. According to Christensen, three that do are a 2% or higher solution of glutaraldehyde, 80% ethyl alcohol or equal parts of bleach and water.

Mary Borg, president of Safelink, a health and safety consultant company in Gainesville, Georgia also notes that you can put the impression into a bag or container with an enzyme cleaner and then into an ultrasonic unit for 10 minutes. She also recommends that you don't use bleach on metal appliances; it can corrode the metal.

After any of the above methods, rinse thoroughly and then follow the generally accepted protocol for disinfection outlined below. However, it's important to note that using any of these solutions or methods may result in distortion of the impression.

Impressions. The following disinfection procedure is geared toward incoming impressions, however, all other incoming prostheses—removable appliances, crowns, bridges, etc.—should be disinfected in the same manner.

Follow the basic disinfection steps outlined above.

Work in a separate area of the lab designated for disinfecting only. "Ideally, the disinfection area should be isolated from the rest of the lab and have stainless steel, impervious surfaces," says Hochhauser, who also notes that there should be no eating, drinking or smoking in the area and no interruption of the technicians during the disinfection process.

Open packaging. If the impression is properly packaged in a sealed bag or other liquid-tight, heat-sealed type of container, you can reuse the outer packaging. If the outer packaging materials are wet or if the impression is not properly packaged, spray disinfect the packaging materials and dispose of them in the regular trash. If you don't disinfect the packaging, it must be disposed of in a container that is closable, leak-proof and labeled as hazardous waste according to BPS regulations.

Hold the impression low in the sink and rinse with running water to rinse off any saliva or disinfectant residue from the dental office. If the residue isn't rinsed off, the impression can continue to absorb it, or it may mix with your own disinfectant, potentially causing distortion.

Remove excess water.

Disinfect. One difficult aspect to disinfecting is that there's no consensus on what solutions or methods to use due to conflicting information on the amount of distortion caused by certain disinfectant/impression-material mixes. Health and safety experts say that more studies—as well as the development of more distortion-resistant impression materials—are needed.

Here are two current approaches to disinfecting:

"The lab needs to know which type of disinfectant the impression material manufacturer recommends," says Borg. This includes knowing the recommended solution, technique (soak or spray) and time frame. Ask your dentist-clients to include the type of impression material used on the prescription.

Christensen suggests disinfecting all impressions by immersing them in a 3.2% glutaraldehyde solution for 30 minutes or in a 2% glutaraldehyde solution for 40 minutes. She notes that using a glutaraldehyde and polyvinyl silicone combination undergoes the least amount of dimensional change, while alginates are notorious for distortion. (For safety tips on working with glutaraldehyde, see Glutaraldehyde precautions below.)

Regardless of which method you use, accurate timing is critical to minimize distortion. According to a June 2000 JADA study, Disinfection and Communication Practices: A Survey of U.S. Dental Laboratories, 20% of laboratories receive impressions bagged in disinfectant and "dentists and laboratories disinfect impressions for longer-than-recommended durations" which can result in distortion and, ultimately, remakes. If you have a client who's having a lot of remakes, ask him if he's timing the process and be sure his impressions aren't arriving bagged in disinfectant.

In addition, if you're like other cost-conscious lab owners, you may be choosing spray disinfectants in order to use less solution and ultimately save money. However, this may not be the best area in which to cut corners. As a general rule of thumb, spraying—though better than nothing—is not as effective as soaking because it may not reach all surfaces of the impression. Christensen also notes that since spray disinfectants are toxic, they can irritate the respiratory system.

After disinfecting, rinse under running water.

Remove excess water by air drying or drying with compressed air into a plastic-lined garbage can.

Note: Impressions that arrive with embedded appliances or items mounted on casts must be disinfected again after the items have been separated.

Repairs or relines. In addition to disinfecting upon receipt, once you've completed grinding, you must disinfect again, following the same steps. In addition, here are some tips to help you prevent cross contamination:

Use suction when grinding. Be sure to use a vacuum system that's in good working order and cleaned regularly.

Keep the area and tools for pumicing and polishing separate from new work.

Add disinfectant to the pumice.

Change and disinfect all tools between cases.

Pre-measure pumice into small paper cups for each case and never reuse it.

Bacteria breed in warm, dark, damp environments and pressure or repair pots meet all three criteria. Rather than putting a denture repair or other appliance directly into a pressure pot, put the appliance into a bag or other container with water and place into the pot. If repairs are not contained in this manner, disinfect the pot between repairs.

If a case is sent for try-in, remember to disinfect it when it's returned to the lab.

Fractured ceramic crowns or bridges must be decontaminated prior to grinding or dressing back. Safelink recommends immersing in an appropriate disinfectant or placing in a porcelain furnace at 350°F for one hour.

Shade guides, brushes, stain palettes and any other items that may have been exposed to contamination by the patient must be disinfected upon receipt. Use the general procedure outlined under "Impressions".

Clinically poured models. Disinfecting clinically poured models is difficult because the model may contain infectious organisms. A generally accepted protocol is to soak it for 10 minutes in iodophore, a quaternary (quat) ammonium chloride-containing product or other quat solution. It's important not to use a disinfectant that will distort the model. Technicians should look for any sign of distortion like pitting or powdery residue. When trimming the dies, employees should wear dust masks and protective eyeware, use an adequate dust collection system and wash their hands before and after trimming.

Outgoing cases should be disinfected prior to going back to the dental office—there is a potential for cases to be contaminated as they travel through the lab.

Follow the basic disinfection steps outlined above.

Rinse the finished restoration under running water.

Disinfect. Follow your particular disinfectant manufacturer's recommended technique and time frame. Christensen recommends using the same glutaraldehyde method as described earlier for incoming impressions. One exception: indirect resin restorations. "The coloring agents in glutaraldehyde could be absorbed and result in discoloration," says Christensen. For these restorations, she recommends simply spraying with Lysol.

If a crown has to go back to the dental office mounted on the model, be sure to spray-disinfect the model as well.

Glutaraldehyde precautions

If your laboratory is working with glutaraldehyde, there are certain precautions you need to take:

Glutaraldehyde is toxic, strongly irritating to the nose, eyes and skin and can cause allergic contact dermatitis. Be sure to work in a properly ventilated area and wear the proper personal protective equipment. Since the chemical can break down latex gloves, try vinyl or nitrile gloves instead.

Do not use spray glutaraldehyde products.

Read over your material safety data sheet (MSDS) for other precautions that may be specific to your chemical.

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